The present invention relates to a connector constituted by a socket contact and a pin contact or printed-circuit board contact plug portion (hereinafter generically called "pin contact") fitted into a socket contact, and particularly relates to a structure of a pin contact having a low insertion force connection.
A known connector is generally constituted by a socket contact and a pin contact which has an inclined portion to be inserted into the socket contact while forcedly opening a contact spring portion formed in the socket contact, and a parallel portion which touches a contact portion of the contact spring portion when the pin contact is fitted into the socket contact.
FIG. 10 shows a general structure of such a connector. In FIG. 10, a pin contact 102 is fitted into a socket contact 101. The socket contact 101 has at least one contact spring portion 110 disposed at any one of the upper, lower, left and right of the socket contact 101 and uses a portion 101a as a fulcrum, and a contact portion (projection portion) 109 shaped like a circular arc and formed in the neighborhood of the contact spring portion 110. The pin contact 102 has a parallel portion 103, and an inclined portion 108 in which a region from a point 105 in the parallel portion 103 to a top end portion of the pin contact 102 is inclined at a constant angle .theta.. At the time of insertion, this pin contact 102 is inserted into the socket contact 101 while the contact portion 109 of the socket contact 101 is forcedly opened by the inclined portion 108 at a top end of the pin contact 102. In a fitted state, the parallel portion 103 having a predetermined external diameter touches the contact portion 109. In FIG. 10, the reference character F designates the insertion force of the pin contact 102, and the reference character P designates the elastically restoring force of the contact portion 109.
If a structure as shown in FIG. 10 is used merely as a pin contact structure, the total insertion force of a connector increases correspondingly to the increase of the number of pins in the connector. Because the size and density of electric parts have been increased recently, the number of pins has been further increased. Assuming now that, for example, the insertion force of a connector having one pin contact as shown in FIG. 10 is 100 g, then the total insertion force of a connector having 1,000 pin contacts is 100 kg which is 1,000 times as much as the insertion force of 100 g. The total insertion force of a connector having 10,000 pin contacts would be 1,000 kg. Because the increase of the total insertion force has an influence not only on "difficulty of insertion" but also on the strength and mount space of electric parts to be connected by the connector, this may become a problem in connection with electric appliances. Accordingly, reduction of the insertion force of the connector becomes an important factor.
A structure of a contact plug portion of a printed-circuit board to attain a reduction of the insertion force, is disclosed in JPB-58-57871. As shown in FIG. 11, the structure is designed so that an inclined portion 208 of a contact 202 in a contact plug portion of a printed-circuit board is shaped like a curve represented by the expression: ##EQU1## in which X is a distance in a direction parallel to a parallel portion 203 by reference (reference point B) to a point (contact point) at which the contact 202 first touches a contact spring portion of a socket contact (not shown) when inserted into the socket contact, Y is a distance in a direction perpendicular to the parallel portion 203 by reference to a point B, (X.sub.0 and Y.sub.0) are the coordinates of a boundary point between the inclined portion 208 and the parallel portion 203, .mu. is a dynamic friction coefficient between the socket contact and the parallel portion 203, and A is a constant determined by X.sub.0, Y.sub.O and .mu.. In the structure of a contact plug portion of a printed-circuit board according to JP-B-58-5787 the inclined portion 208 has a sharp inclination in the area of its pointed end portion and the inclination becomes gentle as the position approaches the parallel portion 203. With By this structure, the insertion force F can be kept constant and the maximum value of the insertion force F can be reduced to about 1/2 compared with the constant inclined portion 108 shown in FIG. 10. The contact 202 is supported by a fixing mold 214 to thereby form a printed-circuit board contact plug portion.